Publications by authors named "Frans N van de Vosse"

99 Publications

Continuum modeling of thrombus formation and growth under different shear rates.

J Biomech 2022 Jan 4;132:110915. Epub 2022 Jan 4.

Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands. Electronic address:

Obstruction of blood flow due to thrombosis is a major cause of ischemic stroke, myocardial infarction, and in severe cases, mortality. In particular, in blood wetting medical devices, thrombosis is a common reason for failure. The prediction of thrombosis by understanding signaling pathways using computational models, lead to identify the risk of thrombus formation in blood-contacting devices and design improvements. In this study, a mathematical model of thrombus formation and growth is presented. A biochemical model of platelet activation and aggregation is developed to predict thrombus size and shape at the site of vascular injury. Computational fluid dynamics using the finite volume method is employed to compute the velocity and pressure fields which are influenced by the growing thrombi. The passive transport of platelets, agonists, the platelet activation kinetics, their adhesion to the growing thrombi and embolization of platelets are solved by a fully coupled set of convection-diffusion-reaction equations. The thrombogenic surface representing blood-contacting material or injured blood vessel was incorporated into the model as a surface flux boundary condition to initiate thrombus formation. The blood is considered as a Newtonian fluid, while the thrombus is treated as a porous medium. The results are compared with in vitro experiments of a microfluidic chamber at an initial inlet venous shear rate of 200s using a pressure-inlet boundary condition. The thrombus development due to agonist concentrations and change in the shear rate as well as thromboembolism for this benchmark problem is successfully computed. Furthermore, to extend the current model to a physiologically relevant configuration, thrombus formation in a blood tube is simulated. Two different heterogeneous reaction rates for platelet aggregation are used to simulate thrombus growth under a constant inlet flow rate. The findings show that the thrombus shape can be substantially altered by the hemodynamic conditions, increase in the shear rate and due to the combined effects of shear induced platelet activation and the heterogeneous reaction rates. It is also concluded that the model is able to predict thrombus formation in different physiological and pathological hemodynamics.
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http://dx.doi.org/10.1016/j.jbiomech.2021.110915DOI Listing
January 2022

Corrections to "Multiperspective Ultrasound Strain Imaging of the Abdominal Aorta".

IEEE Trans Med Imaging 2021 12;40(12):3968

In the above article [1], one error, (1), was found which has an impact on the results and interpretation of the image quality that was described in four sentences, (2)-(5). This correction does not mitigate the overall conclusion of this work, but does positively support improvements of the proposed method (multi-perspective ultrafast imaging) in comparison with the standard method (focused line-by-line imaging).
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http://dx.doi.org/10.1109/TMI.2021.3093104DOI Listing
December 2021

Ultrasound-Based Fluid-Structure Interaction Modeling of Abdominal Aortic Aneurysms Incorporating Pre-stress.

Front Physiol 2021 13;12:717593. Epub 2021 Aug 13.

Photoacoustics & Ultrasound Laboratory Eindhoven (PULS/e), Department of Biomechanical Engineering, Eindhoven University of Technology, Eindhoven, Netherlands.

Currently, the prediction of rupture risk in abdominal aortic aneurysms (AAAs) solely relies on maximum diameter. However, wall mechanics and hemodynamics have shown to provide better risk indicators. Patient-specific fluid-structure interaction (FSI) simulations based on a non-invasive image modality are required to establish a patient-specific risk indicator. In this study, a robust framework to execute FSI simulations based on time-resolved three-dimensional ultrasound (3D+t US) data was obtained and employed on a data set of 30 AAA patients. Furthermore, the effect of including a pre-stress estimation (PSE) to obtain the stresses present in the measured geometry was evaluated. The established workflow uses the patient-specific 3D+t US-based segmentation and brachial blood pressure as input to generate meshes and boundary conditions for the FSI simulations. The 3D+t US-based FSI framework was successfully employed on an extensive set of AAA patient data. Omitting the pre-stress results in increased displacements, decreased wall stresses, and deviating time-averaged wall shear stress and oscillatory shear index patterns. These results underline the importance of incorporating pre-stress in FSI simulations. After validation, the presented framework provides an important tool for personalized modeling and longitudinal studies on AAA growth and rupture risk.
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http://dx.doi.org/10.3389/fphys.2021.717593DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8414835PMC
August 2021

A Generalized Approach for Automatic 3-D Geometry Assessment of Blood Vessels in Transverse Ultrasound Images Using Convolutional Neural Networks.

IEEE Trans Ultrason Ferroelectr Freq Control 2021 11 25;68(11):3326-3335. Epub 2021 Oct 25.

Accurate 3-D geometries of arteries and veins are important clinical data for diagnosis of arterial disease and intervention planning. Automatic segmentation of vessels in the transverse view suffers from the low lateral resolution and contrast. Convolutional neural networks are a promising tool for automatic segmentation of medical images, outperforming the traditional segmentation methods with high robustness. In this study, we aim to create a general, robust, and accurate method to segment the lumen-wall boundary of healthy central and peripheral vessels in large field-of-view freehand ultrasound (US) datasets. Data were acquired using the freehand US, in combination with a probe tracker. A total of ±36 000 cross-sectional images, acquired in the common, internal, and external carotid artery ( N = 37 ), in the radial, ulnar artery, and cephalic vein ( N = 12 ), and in the femoral artery ( N = 5 ) were included. To create masks (of the lumen) for training data, a conventional automatic segmentation method was used. The neural networks were trained on: 1) data of all vessels and 2) the carotid artery only. The performance was compared and tested using an open-access dataset. The recall, precision, DICE, and intersection over union (IoU) were calculated. Overall, segmentation was successful in the carotid and peripheral arteries. The Multires U-net architecture performs best overall with DICE = 0.93 when trained on the total dataset. Future studies will focus on the inclusion of vascular pathologies.
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http://dx.doi.org/10.1109/TUFFC.2021.3090461DOI Listing
November 2021

Model-based aortic power transfer: A potential measure for quantifying aortic stenosis severity based on measured data.

Med Eng Phys 2021 04 26;90:66-81. Epub 2021 Feb 26.

Eindhoven University of Technology, Department of Biomedical Engineering, Postbus 513, Eindhoven 5600MB, the Netherlands.

Current aortic stenosis severity grading is based mainly on the local properties of the stenotic valve, such as pressure gradient or jet velocity. Success rates of valve replacement therapy are still suboptimal, so alternative grading of AS should be investigated. We suggest the efficiency of power transfer from the left ventricle to the aorta, as it takes into account heart, valve and circulatory system. Left ventricular and circulatory power were estimated using a 0D model, which was optimised to patient data: left ventricular and aortic pressure, aortic flow and diastolic left ventricular volume. Optimisation was performed using a data assimilation method. These data were available in rest as well as chemically induced exercise for twelve patients. Using this limited data set, we showed that aortic valve efficiency is highly heterogeneous between patients, but also often dependent on the haemodynamic load. This indicates that power transfer efficiency is a highly interesting metric for further research in aortic stenosis.
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http://dx.doi.org/10.1016/j.medengphy.2021.02.009DOI Listing
April 2021

Enhancing Lateral Contrast Using Multi-perspective Ultrasound Imaging of Abdominal Aortas.

Ultrasound Med Biol 2021 03 19;47(3):535-545. Epub 2020 Dec 19.

Photoacoustics & Ultrasound Lab Eindhoven, Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands.

Vascular ultrasound imaging is inherently hampered by low lateral resolution and contrast. Steering of the ultrasound beams can be used to overcome these limitations in superficial artery imaging because the aperture-to-depth ratio is relatively high. However, in arteries located at larger depths, the steered beams do not overlap for larger steering angles. In this study, the ultrasound probe is physically translated over the abdomen to create large angles between acquisitions, while maintaining overlap on the abdominal aorta. In one phantom setup and 11 volunteers, 2-D cross-sectional multi-perspective ultrasound images of the abdominal aorta were acquired using seven angles between -45° and +45°. Automatic registration of the recorded images was performed by automatic feature detection of the aorta and spine. This automatic detection was successful in 62 out of 77 image sets. Compounded multi-perspective images showed an increase of contrast-to-noise ratios from 0.6 ± 0.1 to 1.2 ± 0.2 over the entire heart cycle in volunteers.
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http://dx.doi.org/10.1016/j.ultrasmedbio.2020.09.023DOI Listing
March 2021

A Spatial Near-Field Clutter Reduction Filter Preserving Tissue Speckle in Echocardiography.

IEEE Trans Ultrason Ferroelectr Freq Control 2021 04 26;68(4):979-992. Epub 2021 Mar 26.

Near-field (NF) clutter in echocardiography is depicted as a diffuse haze hindering the visualization of the myocardium and the blood-pool, thereby degrading its diagnostic value. Several clutter filters have been developed, which are limited in patients with contraction motion and rhythm anomalies, and in 3-D ultrasound (US). This study introduces a new NF clutter reduction method, which preserves US speckles required for strain imaging. The filter developed detects the NF clutter region in the spatial frequency domain. The filter employs an oriented, multiscale approach, and assumes the NF clutter to be predominantly present in the highest and lowest bandpass images. These bandpass images were filtered, whilst sparing features in the myocardium and NF clutter-free regions. The performance of the filter was assessed in a volunteer study, in ten 3-D apical and parasternal view acquisitions, and in a retrospective clinical study composed of 20 cardiac patients with different indications for echocardiography. The filter reduced NF clutter in all data sets, whilst preserving all or most of the myocardium. Additionally, it demonstrated a consistent enhancement of image quality, with an increase in contrast of 4.3 dB on average, and generated a clearer myocardial boundary distinction. Furthermore, the speckles were preserved according to the quality index based on local variance, the structural similarity index method, and normalized cross correlation values, being 0.82, 0.92, and 0.95 on average, respectively. Global longitudinal strain measurements on NF clutter reduced images were improved or equivalent compared to the original acquisitions, with an average increase in strain signal-to-noise ratio of 34%.
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http://dx.doi.org/10.1109/TUFFC.2020.3028155DOI Listing
April 2021

Multiperspective Ultrasound Strain Imaging of the Abdominal Aorta.

IEEE Trans Med Imaging 2020 11 28;39(11):3714-3724. Epub 2020 Oct 28.

Current decision-making for clinical intervention of abdominal aortic aneurysms (AAAs) is based on the maximum diameter of the aortic wall, but this does not provide patient-specific information on rupture risk. Ultrasound (US) imaging can assess both geometry and deformation of the aortic wall. However, low lateral contrast and resolution are currently limiting the precision of both geometry and local strain estimates. To tackle these drawbacks, a multiperspective scanning mode was developed on a dual transducer US system to perform strain imaging at high frame rates. Experimental imaging was performed on porcine aortas embedded in a phantom of the abdomen, pressurized in a mock circulation loop. US images were acquired with three acquisition schemes: Multiperspective ultrafast imaging, single perspective ultrafast imaging, and conventional line-by-line scanning. Image registration was performed by automatic detection of the transducer surfaces. Multiperspective images and axial displacements were compounded for improved segmentation and tracking of the aortic wall, respectively. Performance was compared in terms of image quality, motion tracking, and strain estimation. Multiperspective compound displacement estimation reduced the mean motion tracking error over one cardiac cycle by a factor 10 compared to conventional scanning. Resolution increased in radial and circumferential strain images, and circumferential signal-to-noise ratio (SNRe) increased by 10 dB. Radial SNRe is high in wall regions moving towards the transducer. In other regions, radial strain estimates remain cumbersome for the frequency used. In conclusion, multiperspective US imaging was demonstrated to improve motion tracking and circumferential strain estimation of porcine aortas in an experimental set-up.
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http://dx.doi.org/10.1109/TMI.2020.3003430DOI Listing
November 2020

Uncertainty in model-based treatment decision support: Applied to aortic valve stenosis.

Int J Numer Method Biomed Eng 2020 10 5;36(10):e3388. Epub 2020 Aug 5.

Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, the Netherlands.

Patient outcome in trans-aortic valve implantation (TAVI) therapy partly relies on a patient's haemodynamic properties that cannot be determined from current diagnostic methods alone. In this study, we predict changes in haemodynamic parameters (as a part of patient outcome) after valve replacement treatment in aortic stenosis patients. A framework to incorporate uncertainty in patient-specific model predictions for decision support is presented. A 0D lumped parameter model including the left ventricle, a stenotic valve and systemic circulatory system has been developed, based on models published earlier. The unscented Kalman filter (UKF) is used to optimize model input parameters to fit measured data pre-intervention. After optimization, the valve treatment is simulated by significantly reducing valve resistance. Uncertain model parameters are then propagated using a polynomial chaos expansion approach. To test the proposed framework, three in silico test cases are developed with clinically feasible measurements. Quality and availability of simulated measured patient data are decreased in each case. The UKF approach is compared to a Monte Carlo Markov Chain (MCMC) approach, a well-known approach in modelling predictions with uncertainty. Both methods show increased confidence intervals as measurement quality decreases. By considering three in silico test-cases we were able to show that the proposed framework is able to incorporate optimization uncertainty in model predictions and is faster and the MCMC approach, although it is more sensitive to noise in flow measurements. To conclude, this work shows that the proposed framework is ready to be applied to real patient data.
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http://dx.doi.org/10.1002/cnm.3388DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7583387PMC
October 2020

A demonstration of high field-of-view stability in hands-free echocardiography.

Cardiovasc Ultrasound 2020 May 29;18(1):18. Epub 2020 May 29.

Department of Biomedical Engineering, Eindhoven University of Technology, Groene Loper, Building 15, Eindhoven, The Netherlands.

Background: Exercise stress echocardiography is clinically used to assess cardiovascular diseases. For accurate cardiac evaluation, a stable field-of-view is required. However, transducer orientation and position are difficult to preserve. Hands-free acquisitions might provide more consistent and reproducible results. In this study, the field-of-view stability and variability of hands-free acquisitions are objectively quantified in a comparison with manually obtained images, based on image structural and feature similarities. In addition, the feasibility and consistency of hands-free strain imaging is assessed.

Methods: In twelve healthy males, apical and parasternal images were acquired hands-free, using a fixation device, and manually, during semi-supine exercise sessions. In the final ten seconds of every exercise period, the image structural similarity and cardiac feature consistency were computed using a steerable pyramid employing complex, oriented wavelets. An algorithm discarding images displaying lung artifacts was created. Hands-free strain consistency was analyzed.

Results: Hands-free acquisitions were possible in 9 of the 12 subjects, whereas manually 10 out of 12 could be imaged. The image structural similarity was significantly improved in the hands-free apical window acquisitions (0.91 versus 0.82), and at least equally good in the parasternal window (0.90 versus 0.82). The change in curvature and orientation of the interventricular septum also appeared to be lower in the hands-free acquisitions. The variability in field-of-view was similar in both acquisitions. Longitudinal, septal strain was shown to be at least as consistent when obtained hands-free compared to manual acquisitions.

Conclusions: The field-of-view was shown to be more or equally stable and consistent in the hands-free data in comparison to manually obtained images. The variability was similar, thus respiration- and exercise-induced motions were comparable for manual and hands-free acquisitions. Additionally, the feasibility of hands-free strain has been demonstrated. Furthermore, the results suggest the hands-free measurements to be more reproducible, though further analysis is required.
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http://dx.doi.org/10.1186/s12947-020-00201-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7260740PMC
May 2020

Quantification of the temperature gradient through a catheter in continuous infusion thermodilution for coronary flow measurements.

Physiol Meas 2020 08 11;41(7):075006. Epub 2020 Aug 11.

Catharina Hospital, Eindhoven, The Netherlands.

Objective: Quantifying the absolute coronary blood flow can be done using continuous infusion thermodilution requiring a dedicated infusion catheter. Up to now, there has been little insight into the effect of small variabilities in the physical parameters on the temperature gradient along this catheter. The key goal of this study is to develop and validate a computer model that predicts the temperature of the infusion fluid at the infusion site of the infusion catheter. A secondary goal is to gain insight into the influence of physical variations for the individual patient on the calculated blood flow rate.

Approach: A numerical model of the temperature in the catheter was built using the convection-diffusion equation and validated using an in vitro setup. A sensitivity analysis was performed to investigate the influence of the catheter path inside the body and the temperature of the infusion fluid at different infusion rates. These results were compared to in vivo measurements of 94 patients. Finally, the variation in the computed blood flow rate is estimated considering an average patient, using small variations in the physical parameters.

Main Results: The computed temperature corresponded well with the in vitro measurements, since a maximal difference of 1.5% was observed. The length of the catheter path inside the body had the most influence on the temperature of the infusion fluid at the infusion site. Moreover, temperatures from the numerical model were similar to the results from in vivo measurements. By varying the length of the catheters with 0.04 m, the largest deviation in the calculated blood flow was 33.3 ml/min.

Significance: Insight is gained into the influence of physical variations on the temperature of the infusion fluid at the infusion site of the catheter using thermodilution. The developed numerical model can possibly be used to reduce time in estimating the blood flow rate.
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http://dx.doi.org/10.1088/1361-6579/ab979dDOI Listing
August 2020

3D-printed stenotic aortic valve model to simulate physiology before, during, and after transcatheter aortic valve implantation.

Int J Cardiol 2020 08 4;313:32-34. Epub 2020 May 4.

Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, the Netherlands.

Aims: Pressure loss versus transvalvular flow analysis challenges physiologic models of current aortic valve stenosis. New conceptual frameworks are needed to explain these real-world observations.

Methods And Results: A patient-specific, 3D-printed, silicon model of a stenotic valve was placed inside an in-vitro haemodynamic model of the circulatory system. Instantaneous pressure and flow in the aorta and left ventricle were simulated according to measured patient specific parameters. Thereafter, a realistic transcatheter aortic valve was implanted (TAVI) in the model. Simulated post-TAVI mean pressure gradients resembled patient observations (3.7 ± 0.7 mmHg vs 6.7 ± 2.3 mmHg), but pre-TAVI measurements underestimated the pressure gradient (35.1 ± 0.6 mmHg vs 45.3 ± 1.5 mmHg).

Conclusion: Patient-specific 3D-printed stenotic aortic valve models could simulate baseline haemodynamics. A TAVI procedure was successfully performed on the 3D silicone rubber valve in a physiologic in-vitro model. Pre-TAVI haemodynamics in the model underestimated in-patient mean pressure gradient, whereas post TAVI pressure gradient was predicted correctly with the TAVI valve inside the 3D printed model. This study shows that these types of models could be used to study AS hemodynamics with the TAVI valve inside the 3D printed model. Improvements in the 3D-printed model, like addition of calcification and fine-tuning of the haemodynamic model, could further enhance accuracy of the simulation.
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http://dx.doi.org/10.1016/j.ijcard.2020.04.087DOI Listing
August 2020

Ultrasound-based estimation of remaining cardiac function in LVAD-supported ex vivo hearts.

Artif Organs 2020 Aug 18;44(8):E326-E336. Epub 2020 Apr 18.

Cardiovascular Biomechanics group, Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands.

Left ventricular assist devices (LVAD) provide cardiac support to patients with advanced heart failure. Methods that can directly measure remaining LV function following device implantation do not currently exist. Previous studies have shown that a combination of loading (LV pressure) and deformation (strain) measurements enables quantitation of myocardial work. We investigated the use of ultrasound (US) strain imaging and pressure-strain loop analysis in LVAD-supported hearts under different hemodynamic and pump unloading conditions, with the aim of determining LV function with and without LVAD support. Ex vivo porcine hearts (n = 4) were implanted with LVADs and attached to a mock circulatory loop. Measurements were performed at hemodynamically defined "heart conditions" as the hearts deteriorated from baseline. Hemodynamic (including LV pressure) and radio-frequency US data were acquired during a pump-ramp protocol at speeds from 0 (with no pump outflow) to 10 000 revolutions per minute (rpm). Regional circumferential (ε ) and radial (ε ) strains were estimated over each heart cycle. Regional ventricular dyssynchrony was quantitated through time-to-peak strain. Mean change in LV pulse pressure and ε between 0 and 10 krpm were -21.8 mm Hg and -7.24% in the first condition; in the final condition -46.8 mm Hg and -19.2%, respectively. ε was not indicative of changes in pump speed or heart condition. Pressure-strain loops showed a degradation in the LV function and an increased influence of LV unloading: loop area reduced by 90% between 0 krpm in the first heart condition and 10 krpm in the last condition. High pump speeds and degraded condition led to increased dyssynchrony between the septal and lateral LV walls. Functional measurement of the LV while undergoing LVAD support is possible by using US strain imaging and pressure-strain loops. This can provide important information about remaining pump function. Use of novel LV pressure estimation or measurement techniques would be required for any future use in LVAD patients.
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http://dx.doi.org/10.1111/aor.13693DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7496524PMC
August 2020

Reproducibility assessment of ultrasound-based aortic stiffness quantification and verification using Bi-axial tensile testing.

J Mech Behav Biomed Mater 2020 03 19;103:103571. Epub 2019 Dec 19.

Cardiovascular Biomechanics Group, Department of Biomedical Engineering, Eindhoven University of Technology, P.O. Box 513, 5600, MB, the Netherlands. Electronic address:

Current guidelines for abdominal aortic aneurysm (AAA) repair are primarily based on the maximum diameter. Since these methods lack robustness in decision making, new image-based methods for mechanical characterization have been proposed. Recently, time-resolved 3D ultrasound (4D US) in combination with finite element analysis was shown to provide additional risk estimators such as patient-specific peak wall stresses and wall stiffness in a non-invasive way. The aim of this study is to: 1) assess the reproducibility of this US-based stiffness measurement in vitro and in vivo, and 2) verify this 4D US stiffness using the gold standard: bi-axial tensile testing of the excised aortic tissue. For the in vitro study, 4D US data were acquired in an idealized inflation experiment using porcine aortas. The full aortic geometry was segmented and tracked over the cardiac cycle, and afterwards finite element analysis was performed by calibrating the finite element model to the measured US displacements to find the global aortic wall stiffness. For verification purposes, the porcine tissue was subjected to bi-axial tensile testing. Secondly, four AAA patients were included and 4D US data were acquired before open aortic surgery was performed. Similar to the experimental approach, the 4D US data were analyzed using the iterative finite element approach. During surgery, aortic tissue was harvested and the resulting tissue specimens were analyzed using bi-axial tensile testing. Finally, reproducibility was quantified for both methods. A high reproducibility was observed for the wall stiffness measurements using 4D US, i.e., an ICC of 0.91 (95% CI: 0.78-0.98) for the porcine aortas and an ICC of 0.98 (95% CI: 0.84-1.00) for the AAA samples. Verification with bi-axial tensile testing revealed a good agreement for the inflation experiment and a moderate agreement for the AAA patients, partially caused by the diseased state and inhomogeneities of the tissue. The performance of aortic stiffness characterization using 4D US revealed overall a high reproducibility and a moderate agreement with ex vivo mechanical testing. Future research should include more patient samples, to statistically assess the accuracy of the current in vivo method, which is not trivial due to the low number of open surgical interventions.
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http://dx.doi.org/10.1016/j.jmbbm.2019.103571DOI Listing
March 2020

A novel technique for the assessment of mechanical properties of vascular tissue.

Biomech Model Mechanobiol 2020 Oct 24;19(5):1585-1594. Epub 2020 Jan 24.

Department of Biomedical Engineering, Eindhoven University of Technology, PO Box 513, 5600MB, Eindhoven, The Netherlands.

Accurate estimation of mechanical properties of the different atherosclerotic plaque constituents is important in assessing plaque rupture risk. The aim of this study was to develop an experimental set-up to assess material properties of vascular tissue, while applying physiological loading and being able to capture heterogeneity. To do so, a ring-inflation experimental set-up was developed in which a transverse slice of an artery was loaded in the radial direction, while the displacement was estimated from images recorded by a high-speed video camera. The performance of the set-up was evaluated using seven rubber samples and validated with uniaxial tensile tests. For four healthy porcine carotid arteries, material properties were estimated using ultrasound strain imaging in whole-vessel-inflation experiments and compared to the properties estimated with the ring-inflation experiment. A 1D axisymmetric finite element model was used to estimate the material parameters from the measured pressures and diameters, using a neo-Hookean and Holzapfel-Gasser-Ogden material model for the rubber and porcine samples, respectively. Reproducible results were obtained with the ring-inflation experiment for both rubber and porcine samples. Similar mean stiffness values were found in the ring-inflation and tensile tests for the rubber samples as 202 kPa and 206 kPa, respectively. Comparable results were obtained in vessel-inflation experiments using ultrasound and the proposed ring-inflation experiment. This inflation set-up is suitable for the assessment of material properties of healthy vascular tissue in vitro. It could also be used as part of a method for the assessment of heterogeneous material properties, such as in atherosclerotic plaques.
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http://dx.doi.org/10.1007/s10237-020-01292-wDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7502444PMC
October 2020

Ultrasound Based Wall Stress Analysis of Abdominal Aortic Aneurysms using Multiperspective Imaging.

Eur J Vasc Endovasc Surg 2020 Jan 11;59(1):81-91. Epub 2019 Nov 11.

Cardiovascular Biomechanics Group, Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, the Netherlands. Electronic address:

Background: Current clinical guidelines for surgical repair of abdominal aortic aneurysms (AAAs) are primarily based on maximum diameter assessment. From a biomechanical point of view, not only the diameter but also peak wall stresses will play an important role in rupture risk assessment. These methods require patient specific geometry which typically uses computed tomography (CT) or magnetic resonance imaging. Recently, wall stress analysis based on 3D ultrasound (US) has been proposed, and shows promising results. However, the major limitations in these studies were the use of manual segmentation and the limiting field of view of US. Therefore in this study, the AAA is imaged with multiperspective 3D ultrasound, merged to obtain a large field of view, and afterwards automatically segmented. Geometry and wall stress results were validated using CT imaging.

Methods: Three dimensional US and CT data were available for 40 AAA patients (maximum diameter 34-61 mm). The full US based AAA geometry was determined using automatic segmentation, and when the aneurysm exceeded a single 3D volume, automatic fusion of multiple 3D US volumes was used. Wall stress analysis was performed for all AAA patients and percentile wall stresses were derived. The accuracy of the US based geometry and wall stress prediction was measured by comparison with CT data.

Results: Estimated geometries derived from 3D US and CT data showed good similarity, with an overall median similarity index (SI) of 0.89 and interquartile range of 0.87-0.92, whereas the median Hausdorff distances (HD), a measure for the maximum local mismatch, was 4.6 (4.0-5.9) mm for all AAA geometries. Thereby, the wall stress results based on merged multiperspective 3D US data revealed a greater similarity to CT than single 3D US data.

Conclusion: This study showed that large volume geometry assessment of AAAs using multiperspective 3D ultrasound, segmentation and fusion, and wall stress analysis is feasible in a robust and labour efficient manner.
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http://dx.doi.org/10.1016/j.ejvs.2019.01.026DOI Listing
January 2020

Image acquisition stability of fixated musculoskeletal sonography in an exercise setting: a quantitative analysis and comparison with freehand acquisition.

J Med Ultrason (2001) 2020 Jan 7;47(1):47-56. Epub 2019 Nov 7.

Cardiovascular Biomechanics Group, Department of Biomedical Engineering, Eindhoven University of Technology, Groene Loper, 5612 AP, Eindhoven, The Netherlands.

Purpose: In dynamic musculoskeletal sonography, probe fixation can contribute to field of view (FOV) consistency, which is necessary for valid analysis of architectural parameters. In this volunteer study, the achieved FOV consistency in fixated ultrasonography was quantified and compared with freehand acquisition.

Methods: During five resting periods during cycling exercise, longitudinal B-mode images of the vastus lateralis (VL) muscle were acquired on one thigh with a fixated probe, and by two trained observers on the other thigh. In each acquisition, the structural similarity compared to the first resting period was determined using the complex wavelet structural similarity index (CW-SSIM). Also, the pennation angle of the VL was measured. Both CW-SSIM and pennation angle were compared between fixated and freehand acquisition. Furthermore, the compression of tissue by the probe fixation was measured.

Results: In fixated acquisition, a significantly higher structural similarity (p < 0.05) and an improved repeatability of pennation angle measurement were obtained compared to freehand acquisition. Probe fixation compressed muscle tissue by 12% on average.

Conclusions: Quantification of the structural similarity showed an increase in FOV consistency with sonography compared to freehand acquisition. The demonstrated feasibility of long-term fixated acquisition might be attractive in many medical fields and sports, and for reduction of work-related ergonomic problems among sonographers.
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http://dx.doi.org/10.1007/s10396-019-00983-xDOI Listing
January 2020

Cardiovascular models for personalised medicine: Where now and where next?

Med Eng Phys 2019 10;72:38-48

Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands.

The aim of this position paper is to provide a brief overview of the current status of cardiovascular modelling and of the processes required and some of the challenges to be addressed to see wider exploitation in both personal health management and clinical practice. In most branches of engineering the concept of the digital twin, informed by extensive and continuous monitoring and coupled with robust data assimilation and simulation techniques, is gaining traction: the Gartner Group listed it as one of the top ten digital trends in 2018. The cardiovascular modelling community is starting to develop a much more systematic approach to the combination of physics, mathematics, control theory, artificial intelligence, machine learning, computer science and advanced engineering methodology, as well as working more closely with the clinical community to better understand and exploit physiological measurements, and indeed to develop jointly better measurement protocols informed by model-based understanding. Developments in physiological modelling, model personalisation, model outcome uncertainty, and the role of models in clinical decision support are addressed and 'where-next' steps and challenges discussed.
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http://dx.doi.org/10.1016/j.medengphy.2019.08.007DOI Listing
October 2019

The Role of One-Dimensional Model-Generated Inter-Subject Variations in Systemic Properties on Wall Shear Stress Indices of Intracranial Aneurysms.

IEEE Trans Biomed Eng 2020 04 15;67(4):1030-1039. Epub 2019 Jul 15.

Variations in systemic properties of the arterial tree, such as aging-induced vessel stiffness, can alter the shape of pressure and flow waveforms. As a consequence, the hemodynamics around a cerebral aneurysm change, and therefore, also the corresponding in- and outlet boundary conditions (BCs) used for three-dimensional (3D) calculations of hemodynamic indices. In this study, we investigate the effects of variations in systemic properties on wall shear stress (WSS) indices of a cerebral aneurysm. We created a virtual patient database by varying systemic properties within physiological ranges. BCs for 3D-CFD simulations were derived using a pulse wave propagation model for each realization of the virtual database. WSS indices were derived from the 3D simulations and their variabilities quantified. Variations in BCs, caused by changes in systemic properties, yielded variabilities in the WSS indices that were of the same order of magnitude as differences in these WSS indices between ruptured and unruptured aneurysms. Sensitivity analysis showed that the systemic properties impacted both in- and outlet BCs simultaneously and altered the WSS indices. We conclude that the influence of variations in patient-specific systemic properties on WSS indices should be evaluated when using WSS indices in multidisciplinary rupture prediction models.
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http://dx.doi.org/10.1109/TBME.2019.2928416DOI Listing
April 2020

Echocardiographic Assessment of Left Bundle Branch-Related Strain Dyssynchrony: A Comparison With Tagged MRI.

Ultrasound Med Biol 2019 08 3;45(8):2063-2074. Epub 2019 May 3.

Cardiovascular Biomechanics, Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands.

Recent studies have shown the efficacy of myocardial strain estimated using speckle tracking echocardiography (STE) in predicting response to cardiac resynchronisation therapy. This study focuses on circumferential strain patterns, comparing STE-acquired strains to tagged-magnetic resonance imaging (MRI-T). Second, the effect of regularisation was examined. Two-dimensional parasternal ultrasound (US) and MRI-T data were acquired in the left ventricular short-axis view of canines before (n = 8) and after (n = 9) left bunch branch block (LBBB) induction. US-based strain analysis was performed on Digital Imaging and Communications in Medicine data at the mid-level using three overall methods ("Commercial software," "Basic block-matching," "regularised block-matching"). Moreover, three regularisation approaches were implemented and compared. MRI-T analysis was performed using SinMod. Normalised regional circumferential strain curves, based on standard six or septal/lateral segments, were analysed and cross-correlated with MRI-T data. Systolic strain (SS) and septal rebound stretch (SRS) were calculated and compared. Overall agreement of normalised circumferential strain was good between all methods on a global and regional level. All STE methods showed a bias (≥4% strain) toward higher SS estimates. Pre-LBBB, septal and lateral segment correlation was excellent between the Basic (mean ρ = 0.96) and regularised (mean ρ = 0.97) methods and MRI-T. The Commercial method showed a significant discrepancy between the two walls (septal ρ = 0.94, lateral ρ = 0.68). Correlation with MRI-T reduced between pre- and post-LBBB (Commercial ρ = 0.79, Basic ρ = 0.82, mean regularised ρ = 0.86). Septal strain patterns and SRS varied with the STE software and type of regularisation, with all STE methods estimating non-zero SRS values pre-LBBB. Absolute values showed moderate agreement, with a bias for higher strain from STE. SRS varied with the type of software and extra regularisation applied. Open efforts are needed to understand the underlying causes of differences between STE methods before standardisation can be achieved. This is particularly important given the apparent clinical value of strain-based parameters such as SRS.
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http://dx.doi.org/10.1016/j.ultrasmedbio.2019.03.012DOI Listing
August 2019

A predictive computational model to estimate myocardial temperature during intracoronary hypothermia in acute myocardial infarction.

Med Eng Phys 2019 06 18;68:65-75. Epub 2019 Apr 18.

Department of Biomedical Engineering, Eindhoven University of Technology, The Netherlands.

Hypothermia, if provided before coronary reperfusion, reduces infarct size in animal models of acute myocardial infarction (AMI). Translation to humans has failed so far, because the target temperature is not reached in time within the endangered myocardium using systemic hypothermia method. Hence, a clinically applicable method has been developed to provide intracoronary hypothermia using cold saline, selectively infused locally into the infarct area. In this study, a lumped parameter model has been designed to support the clinical method and to describe this myocardial cooling process mathematically. This model is able to predict the myocardial temperature changes over time, which cannot be measured, based on the temperature and flow of the intracoronary injected cold saline and coronary arterial blood. It was validated using data from an isolated beating porcine heart model and applied on data from patients with AMI undergoing intracoronary hypothermia. In prospect, the computational model may be used as an assistive tool to calculate the patient specific flow rate and temperature of saline required for reliable achievement of the target myocardial temperature in the hypothermia enhanced clinical treatment of AMI.
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http://dx.doi.org/10.1016/j.medengphy.2019.03.011DOI Listing
June 2019

A mathematical model to investigate the effects of intravenous fluid administration and fluid loss.

J Biomech 2019 May 9;88:4-11. Epub 2019 Mar 9.

Department of Biomedical Engineering, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, the Netherlands.

The optimal fluid administration protocol for critically ill perioperative patients is hard to estimate due to the lack of tools to directly measure the patient fluid status. This results in the suboptimal clinical outcome of interventions. Previously developed predictive mathematical models focus on describing the fluid exchange over time but they lack clinical applicability, since they do not allow prediction of clinically measurable indices. The aim of this study is to make a first step towards a model predictive clinical decision support system for fluid administration, by extending the current fluid exchange models with a regulated cardiovascular circulation, to allow prediction of these indices. The parameters of the model were tuned to correctly reproduce experimentally measured changes in arterial pressure and heart rate, observed during infusion of normal saline in healthy volunteers. With the resulting tuned model, a different experiment including blood loss and infusion could be reproduced as well. These results show the potential of using this model as a basis for a decision support tool in a clinical setting.
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http://dx.doi.org/10.1016/j.jbiomech.2019.03.002DOI Listing
May 2019

Including surrounding tissue improves ultrasound-based 3D mechanical characterization of abdominal aortic aneurysms.

J Biomech 2019 03 19;85:126-133. Epub 2019 Jan 19.

Cardiovascular Biomechanics Group, Department of Biomedical Engineering, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, the Netherlands.

Objectives: In this study the influence of surrounding tissues including the presence of the spine on wall stress analysis and mechanical characterization of abdominal aortic aneurysms using ultrasound imaging has been investigated.

Methods: Geometries of 7 AAA patients and 11 healthy volunteers were acquired using 3-D ultrasound and converted to finite element based models. Model complexity of externally unsupported (aorta-only) models was complemented with inclusion of both soft tissue around the aorta and a spine support dorsal to the aorta. Computed 3-D motion of the aortic wall was verified by means of ultrasound speckle tracking. Resulting stress, strain, and estimated shear moduli were analyzed to quantify the effect of adding surrounding material supports.

Results: An improved agreement was shown between the ultrasound measurements and the finite element tissue and spine models compared to the aorta-only models. Peak and 99-percentile Von Mises stress showed an overall decrease of 23-30%, while estimated shear modulus decreased with 12-20% after addition of the soft tissue. Shear strains in the aortic wall were higher in areas close to the spine compared to the anterior region.

Conclusions: Improving model complexity with surrounding tissue and spine showed a homogenization of wall stresses, reduction in homogeneity of shear strain at the posterior side of the AAA, and a decrease in estimated aortic wall shear modulus. Future research will focus on the importance of a patient-specific spine geometry and location.
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http://dx.doi.org/10.1016/j.jbiomech.2019.01.024DOI Listing
March 2019

A comparative study of geometry-based methods and intra-arterial pressure measurements to assess the hemodynamic significance of equivocal iliac artery stenoses.

Vascular 2019 Apr 10;27(2):119-127. Epub 2018 Oct 10.

2 Department of Biomedical Engineering, CARIM School for Cardiovascular Diseases Maastricht University Medical Center, Maastricht, The Netherlands.

Objectives: To date, the ultimate decision to treat iliac artery stenoses in patients suffering from symptomatic peripheral arterial disease is based on the patient's symptoms and on visual inspection of angiographical images. The primary aim of this study was to investigate the accuracy of geometry-based methods (i.e. visual inspection and quantitative vascular analysis (Viewforum version R7.2v1 Advanced vessel analysis, Philips Healthcare, Best, The Netherlands) of 3D rotational angiography) to identify the severity of equivocal iliac artery stenosis in peripheral arterial disease patients with intra-arterial hyperemic pressure measurements (gold standard) as a reference.

Methods: Twenty patients with symptomatic iliac artery stenoses were subjected to 3D rotational angiography. Intra-arterial pressure measurements under hyperemic conditions were performed across 24 visually identified iliac artery stenoses. Three experienced interventional-radiologists retrospectively estimated the lumen diameter reduction by visual inspection. Furthermore, quantitative vascular analysis was performed on the 3D rotational angiography data. Geometry-based estimates were classified into two groups: lumen diameter reduction of <50% (non-significant) and diameter reduction 50% (significant), and compared to the intra-arterial hyperemic pressure gradients. A stenosis causing a pressure gradient (Δp) ≥10 mmHg was considered hemodynamically significant.

Results: Visual inspection and quantitative vascular analysis correctly identified hemodynamically significant stenoses in, respectively, 83% and 67% of the 24 iliac artery stenoses. Quantitative vascular analysis-based identification of hemodynamic significant stenoses (Δp ≥ 10 mmHg) could be optimized by lowering the threshold to a 42% lumen diameter reduction which improved the accuracy from 67% to 83%.

Conclusions: Visual inspection of 3D rotational angiography by experienced interventional-radiologists has an 83% accuracy to identify hemodynamic significant iliac artery stenoses (Δ p ≥10 mmHg). The use of quantitative vascular analysis software did not improve accuracy.
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http://dx.doi.org/10.1177/1708538118805659DOI Listing
April 2019

Quantification of aortic stiffness and wall stress in healthy volunteers and abdominal aortic aneurysm patients using time-resolved 3D ultrasound: a comparison study.

Eur Heart J Cardiovasc Imaging 2019 02;20(2):185-191

Cardiovascular Biomechanics Group, Department of Biomedical Engineering, Eindhoven University of Technology, P.O. Box 513, MB Eindhoven, The Netherlands.

Aims: Using non-invasive 3D ultrasound, peak wall stress (PWS) and aortic stiffness can be evaluated, which may provide additional criteria in abdominal aortic aneurysm (AAA) risk assessment. In this study, these measures were determined in both young and age-matched individuals, and AAA patients while its relation to age, maximum diameter, and growth was assessed statistically.

Methods And Results: Time-resolved 3D-US data were acquired for 30 volunteers and 65 AAA patients. The aortic geometry was segmented, and tracked over the cardiac cycle using 3D speckle tracking to characterize the wall motion. Wall stress analysis was performed using finite element analysis. Model parameters were optimized until the model output matched the measured 3D displacements. A significant increase in aortic stiffness was measured between the age-matched volunteers [median 0.58, interquartile range (IQR) 0.48-0.71 kPa⋅m] and the small AAA patients (median 1.84, IQR 1.38-2.46 kPa⋅m; P < 0.001). In addition, an increase in aortic stiffness was evaluated between the small (30-39 mm) and large (≥50 mm) AAAs (median 2.72, IQR 1.99-3.14 kPa⋅m; P = 0.01). The 99th percentile wall stress showed a positive correlation with diameter (ρ = 0.73, P < 0.001), and significant differences between age-matched volunteers and AAA patients.

Conclusion: The AAA pathology causes an early and significant increase in aortic stiffness of the abdominal aorta, even after correcting for the expected effect of ageing and differences in arterial pressure. Moreover, some AAAs revealed relatively high PWS, although the maximum diameter was below the threshold for surgical repair. Using the current method, these measures become available during follow-up, which could improve AAA rupture risk assessment.
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http://dx.doi.org/10.1093/ehjci/jey051DOI Listing
February 2019

Investigation on the Effect of Spatial Compounding on Photoacoustic Images of Carotid Plaques in the In Vivo Available Rotational Range.

IEEE Trans Ultrason Ferroelectr Freq Control 2018 03;65(3):440-447

Photoacoustic imaging (PAI) is a promising imaging modality due to its high optical specificity. However, the low signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of in vivo PA images are major challenges that prevent PAI from finding its place in clinics. This paper investigates the merit of spatial compounding of PA images in arterial phantoms and the achievable improvements of SNR, when in vivo conditions are mimicked. The analysis of the compounding technique was performed on a polyvinyl alcohol vessel phantom with black threads embedded in its wall. The in vivo conditions were mimicked by limiting the rotation range in ±30°, adding turbid surrounding medium, and filling the lumen with porcine blood. Finally, the performance of the technique was evaluated in ex vivo human carotid plaque samples. Results showed that spatial compounding elevates the SNR by 5-10 dB and CNR by 1-5 dB, depending on the location of the absorbers. This paper elucidates prospective in vivo PA characterization of carotid plaques by proposing a method to enhance PA image quality.
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http://dx.doi.org/10.1109/TUFFC.2018.2792903DOI Listing
March 2018

A Novel Angiographic Quantification of Aortic Regurgitation After TAVR Provides an Accurate Estimation of Regurgitation Fraction Derived From Cardiac Magnetic Resonance Imaging.

JACC Cardiovasc Interv 2018 02 17;11(3):287-297. Epub 2018 Jan 17.

Department of Cardiology, Thoraxcenter, Erasmus University Medical Center, Rotterdam, the Netherlands; Cardialysis Clinical Trials Management and Core Laboratories, Rotterdam, the Netherlands. Electronic address:

Objectives: This study sought to compare a new quantitative angiographic technique to cardiac magnetic resonance-derived regurgitation fraction (CMR-RF) for the quantification of prosthetic valve regurgitation (PVR) after transcatheter aortic valve replacement (TAVR).

Background: PVR after TAVR is challenging to quantify, especially during the procedure.

Methods: Post-replacement aortograms in 135 TAVR recipients were analyzed offline by videodensitometry to measure the ratio of the time-resolved contrast density in the left ventricular outflow tract to that in the aortic root (videodensitometric aortic regurgitation [VD-AR]). CMR was performed within an interval of ≤30 days (11 ± 6 days) after the procedure.

Results: The average CMR-RF was 6.7 ± 7.0% whereas the average VD-AR was 7.0 ± 7.0%. The correlation between VD-AR and CMR-RF was substantial (r = 0.78, p < 0.001). On receiver-operating characteristic curves, a VD-AR ≥10% corresponded to >mild PVR as defined by CMR-RF (area under the curve: 0.94; p < 0.001; sensitivity 100%, specificity 83%), whereas a VD-AR ≥25% corresponded to moderate-to-severe PVR (area under the curve: 0.99; p = 0.004; sensitivity 100%, specificity 98%). Intraobserver reproducibility was excellent for both techniques (for CMR-RF, intraclass correlation coefficient: 0.91, p < 0.001; for VD-AR intraclass correlation coefficient: 0.93, p < 0.001). The difference on rerating was -0.04 ± 7.9% for CMR-RF and -0.40 ± 6.8% for VD-AR.

Conclusions: The angiographic VD-AR provides a surrogate assessment of PVR severity after TAVR that correlates well with the CMR-RF.
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http://dx.doi.org/10.1016/j.jcin.2017.08.045DOI Listing
February 2018

In Vivo Validation of Patient-Specific Pressure Gradient Calculations for Iliac Artery Stenosis Severity Assessment.

J Am Heart Assoc 2017 12 23;6(12). Epub 2017 Dec 23.

Department of Vascular Surgery, St Antonius Hospital, Nieuwegein, The Netherlands.

Background: Currently, the decision to treat iliac artery stenoses is mainly based on visual inspection of digital subtraction angiographies. Intra-arterial pressure measurements can provide clinicians with accurate hemodynamic information. However, pressure measurements are rarely performed because of their invasiveness and the time required. Therefore, the aim of the study was to test the feasibility of a computational model that can predict translesional pressure gradients across iliac artery stenoses on the basis of imaging data only.

Methods And Results: Patients (N=21) with symptomatic peripheral arterial disease and a peak systolic velocity ratio between 2.5 and 5.0 were included in the study. Patients underwent per-procedural 3-dimensional rotational angiography and hyperemic intra-arterial translesional pressure measurements. Vascular anatomical features were reconstructed from the 3-dimensional rotational angiography data into an axisymmetrical 2-dimensional computational mesh, and flow was estimated on the basis of the stenosis geometry. Computational fluid dynamics were performed to predict the pressure gradient and were compared with the measured pressure gradients. A good agreement by overlapping error bars of the predicted and measured pressure gradients was found in 21 of 25 lesions. Stratification of the stenosis on the basis of the predicted pressure gradient into hemodynamic not significant (<10 mm Hg) and hemodynamic significant (≥10 mm Hg) resulted in sensitivity, specificity, and overall predictive values of 95%, 60%, and 88%, respectively.

Conclusions: The feasibility of the patient-specific computational model to predict the hyperemic translesional pressure gradient over iliac artery stenosis was successfully tested. Presented results suggest that, with further optimization and corroboration, the model can become a valuable aid to the diagnosis of equivocal iliac artery stenosis.

Clinical Trial Registration: URL: http://www.trialregister.nl. Unique identifier: NTR5085.
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http://dx.doi.org/10.1161/JAHA.117.007328DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5779042PMC
December 2017

Ultrasound functional imaging in an ex vivo beating porcine heart platform.

Phys Med Biol 2017 Nov 14;62(23):9112-9126. Epub 2017 Nov 14.

Cardiovascular Biomechanics group, Department of Biomedical Engineering, Eindhoven University of Technology, PO Box 513, GEM-Z4.131, 5600 MB Eindhoven, Netherlands.

In recent years, novel ultrasound functional imaging (UFI) techniques have been introduced to assess cardiac function by measuring, e.g. cardiac output (CO) and/or myocardial strain. Verification and reproducibility assessment in a realistic setting remain major issues. Simulations and phantoms are often unrealistic, whereas in vivo measurements often lack crucial hemodynamic parameters or ground truth data, or suffer from the large physiological and clinical variation between patients when attempting clinical validation. Controlled validation in certain pathologies is cumbersome and often requires the use of lab animals. In this study, an isolated beating pig heart setup was adapted and used for performance assessment of UFI techniques such as volume assessment and ultrasound strain imaging. The potential of performing verification and reproducibility studies was demonstrated. For proof-of-principle, validation of UFI in pathological hearts was examined. Ex vivo porcine hearts (n  =  6, slaughterhouse waste) were resuscitated and attached to a mock circulatory system. Radio frequency ultrasound data of the left ventricle were acquired in five short axis views and one long axis view. Based on these slices, the CO was measured, where verification was performed using flow sensor measurements in the aorta. Strain imaging was performed providing radial, circumferential and longitudinal strain to assess reproducibility and inter-subject variability under steady conditions. Finally, strains in healthy hearts were compared to a heart with an implanted left ventricular assist device, simulating a failing, supported heart. Good agreement between ultrasound and flow sensor based CO measurements was found. Strains were highly reproducible (intraclass correlation coefficients  >0.8). Differences were found due to biological variation and condition of the hearts. Strain magnitude and patterns in the assisted heart were available for different pump action, revealing large changes compared to the normal condition. The setup provides a valuable benchmarking platform for UFI techniques. Future studies will include work on different pathologies and other means of measurement verification.
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http://dx.doi.org/10.1088/1361-6560/aa9515DOI Listing
November 2017

Videodensitometric quantification of paravalvular regurgitation of a transcatheter aortic valve: in vitro validation.

EuroIntervention 2018 01;13(13):1527-1535

Department of Cardiology, Academic Medical Center, University of Amsterdam, Amsterdam, the Netherlands.

Aims: Videodensitometric assessment of aortography provides a periprocedural quantitation of prosthetic valve regurgitation (PVR) after transcatheter aortic valve implantation. We sought to compare the videodensitometric parameters of PVR severity to the regurgitation fraction (RF) in a controlled in vitro setting.

Methods And Results: In a mock circulation system, a transcatheter balloon-expandable valve inserted at the aortic valve position was gradually deformed to induce different grades of paravalvular leakage and the RF was measured with a transonic flow probe. Contrast aortography was performed and the following videodensitometric parameters were generated: left ventricle aortic regurgitation (LV-AR), LV outflow tract AR (LVOT-AR), quantitative regurgitation assessment (qRA) index, relative maximum density (relative max), and maximum upslope of the LV time-density curve. The correlation was substantial between videodensitometric parameters (LV-AR, LVOT-AR, qRA index, relative max, and maximum upslope) and RF (r2=0.96, 0.96, 0.93, 0.87, and 0.93; p<0.001 for all). LV-AR (region of interest [ROI]=entire LV) and LVOT-AR (ROI=LVOT) were not different (p=0.51) and were strongly correlated (r2=0.99) with a mean difference of 1.92% (95% limits of agreement: ±2.83). The correlations of LV-AR and LVOT-AR with RF were stronger when more than one cardiac cycle was included in the analysis (one cycle: r2=0.85 and r2=0.83; four cycles: r2=0.96 and r2=0.96, for LV-AR and LVOT-AR, respectively). Including more cycles beyond four did not improve accuracy.

Conclusions: Quantitative assessment of PVR by videodensitometry of aortograms strongly correlates with the actual RF in a controlled in vitro setting. Accuracy is improved by including more than one cardiac cycle in the analysis.
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http://dx.doi.org/10.4244/EIJ-D-17-00595DOI Listing
January 2018
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